It is known that, in a dynamic operational environment, the proper management of the flight of an aircraft resides in essence in the capacity of the crew to adjust and control the trajectory followed and the associated speed profile.
Most aircraft have means allowing the control and maintenance of flight parameters with the aid of an automatic piloting system. This system allows, for example, the maintenance of an altitude, of a speed, of a vertical speed, of a heading, etc. Aircraft fitted with an automatic piloting system which makes it possible to follow guidance setpoints in an automatic manner, are provided with an item of equipment (or control unit), called an FCU (“Flight Control Unit”) on airplanes of AIRBUS type and an MCP (“Mode Control Panel”) on airplanes of BOEING type, which allows a pilot of the airplane to enter guidance setpoints into the guidance system. Generally, the pilot chooses a guidance setpoint, and then he commands the engagement (activation) of the associated guidance mode, so that it takes into account either the value entered (in a so-called “selected” mode), or a value calculated by the system according to diverse criteria (as for example in the particular case of following a preprogrammed flight plan).
A key element of the process for managing the servocontrolled trajectory and the speed is therefore the transmission of the crew's intentions to the onboard systems of the aircraft.
The management of the aircraft's vertical flight plan involves problematic issues of managing the total energy, combination of the potential energy (related to the altitude) and of the kinetic energy (related to the speed). Any modification of the trajectory in the vertical plane will have an impact on the evolution of the speed of the aircraft and vice versa, the modification of the total energy of the aircraft being limited and given by the aerodynamic and propulsive performance of the aircraft.
In a dynamic operational environment, it may happen that the crew wishes to rapidly modify the altitude of the aircraft or else its speed, as well as the way in which the aircraft will achieve this or these new objectives. The crew may need to know at which horizon, namely at which distance ahead of the aircraft along the servocontrolled trajectory, the aircraft will actually attain these objectives, which horizon depends on the performance of the aircraft.
For example, the aircraft may have:                to enter an airspace at a maximum imposed speed; or        to leave its initial flight level so as to achieve a lower flight level before a given distance, doing so in order to satisfy constraints of separability with other aircraft flying at this initial flight level.        
Though the automatic piloting systems and the associated interfaces make it possible to modify the setpoints of the trajectory in the vertical plane (altitude or speed), the interfaces do not make it possible to view directly where the aircraft is going or only in a partial and approximate manner. Moreover, the onboard systems for automated flight management do not offer the possibility of directly adjusting the position at which these speed and altitude objectives are attained.
The object of the present invention is to remedy the aforementioned drawbacks. It relates to a method for aiding the management of the flight of an aircraft, in particular of a transport airplane, which allows in particular the crew to manage by objective the changes of speed and the changes of altitude of the aircraft.